Method for removing water from formaldehyde



3,l69,840 Patented Feb. 16, 1965 Connecticut No Drawing. Filed Nov. 4, 1963, Ser. No. 321,336 4 Claims. (Cl. 5529) 7 The present invention relates to the drying of formaldehyde, and more specifically to a simple one-step process for removing small amounts of water from a formaldehyde gas stream.

It is generally known that Water seriously interferes with the polymerization of formaldehyde to form high molecular weight polyoxymethylene polymers. As little as 0.1% by weight of Water will frequently prevent the formation of consistently high molecular weight products.

Numerous methods have been suggested in the prior art to dry formaldehyde. These methods utilize both physical and chemical means. However, due to the fact that formaldehyde has a great afiinity for water, and is extremely reactive toward practically all efficient desiccants, only the most complex physical separation plants, and practically no desiccants have proven satisfactory for wide scale application.

It is therefore an object of the present invention to provide an improved method for drying formaldehyde.

It is another object to provide a desiccant for extracting substantially all water from formaldehyde which is substantially non-reactive toward formaldehyde.

These andstill further objects of the present invention will become readily apparent to one skilled in the art through the following detailed description and specific examples.

Broadly, the present invention contemplates a method for drying formaldehyde which comprises passing a gaseous stream of a water contaminated formaldehyde through liquid dimethylsulfoxide maintained at a temperature of from about 20 to about 110 C. and preferably at from 50 to 100 C. v

Mode specifically, I have found that practically the last traces of water contained in a formaldehyde gas stream may be quickly and conveniently removed by contracting the formaldehyde with dimethylsulfoxide which is maintained preferably at a temperature from about 50 to about 100 C., and which preferably contains below about by weight of water dissolved therein. Gaseous formaldehyde which-has been dried in this manner may be easily polymerized to form high molecular weight polymers using any one of numerous polymerization catalyst and processes well known to those skilled in the art.

Gaseous formaldehyde which is treated in accordance with the present invention, may possess practically any water content. However, since a given amount of dimethylsulfoxide will absorb only a certain amount of water, it is preferred to have a formaldehyde gas stream containing as little water as possible. In this manner less dimethylsulfoxide is required for a given drying operation. Generally speaking, it is preferred to have an incoming formaldehyde gas containing not more than about 5% by weight of Water. Such a formaldehyde gas stream may be readily obtained by pyrolysis of paraformaldehyde which generally results in a formaldehyde gas containing from about 3 to about 5% by weight of water. It is also possible to utilize formaldehyde gas stream obtained by any one of the commercially used processes for synthesizing formaldehyde gas. Furthermore, gaseous streams which have been previously treated by mechanical separation procedures to remove large amounts of water may also be effectively treated in accordances with the teachings of the present invention.

Dimethylsulfoxide which is used in carrying out the present invention preferably contains below about 5% by weight of water. Dimethylsulfoxide containing below this amount of water will elfectively scavenge water from an incoming formaldehyde gas stream. If a substantially anhydrous dimethylsulfoxide is used in the practice of the invention it is found that up to about 0.05 g. of water per gram of dimethylsulfoxide used may be absorbed from an incoming formaldehyde gas stream before the dimethly sulfoxide becomes saturated to a degree wherein it no longer is capable of removing substantially all the water from the formaldehyde gas stream. Once the di me'thylsulfoxide has absorbed the maximum amount of water, that is, about 5% by weight of water, it may be conveniently dried by heating to a temperature of from about to C. to drive off water and any residual formaldehyde which may be entrained in the dimethylsulfoxide.

The dimethylsulfoxide which is used to absorb water from formaldehyde is maintained at a preferred temperature of from about 50 to about 100 C. It is found that in this temperature range, dimethylsulfoxide will extract water from the formaldehyde gas stream in a minimum amount of time. In a preferred method for conducting the drying operation, formaldehyde gas is simply bubbled through a liquid body of dimethylsulfoxide contained at the required temperature. The exact time that the formaldehyde gas stream is in contact with the dimethyL' sulfoxide it is dependent upon the efiiciency of the par-i ticular contact apparatus or system used. That is, if the formaldehyde gas is contacted in the form of very fine bubbles, it is found that absorption of the water occurs in a shorter time than if the larger gas bubbles are passed through the dimethylsulfoxide mass.

In its simplest form, the apparatus used to conduct the present process maycomprise a simple cylinder having a gas inlet at the bottom and an outlet at the top. Dimethylsulfoxide is maintained within the cylinder at the desired temperature and the formaldehyde gas is passed under pressure into the bottom of the cylinder. As the formaldehyde gas bubbles up through the dimethylsulfoxide, water is-absorbe'd therefrom and dried formaldehyde gas passes from the top of the cylinder. Obviously, the present invention is notrestricted to the use of the aforementioned apparatus and any commercially available liquid-gas contact apparatus may be effectively used.

The formaldehyde gas which is dried by the aforementioned contact with dimethylsulfoxide contains only trace amounts of water. The actual amount of water which remains in the formaldehyde gas depends to,

some extent on the contact time with dimethylsulfoxide as well as the water content dimethylsulfoxide used. The actual amount of dehydration required'for' a 'givenfdrying operation will depend on the ultimate use to which the.

formaldehyde gas is to be put.

Generally speaking, when the formaldehyde gas is to be used in subsequent polymerizations, it is found that a water content from about 0.01 to about 0.1% is permissible. Obviously, commercial consideration will frequently govern the particular degree of Water removal which must be achieved.

Throughout the processing of the formaldehyde gas stream, it is generally preferred to maintain it at a minimum temperature of about 70 to 90 C. It is found that the formaldehyde gas will spontaneously polymerize at temperatures below this range. This spontaneously polymerized formaldehyde will serve to clog handling conduits as well as cause decrease percentage yield of dried formaldehyde gas.

l L ofthe second reaction vessel.

'- In the event that the formaldehyde dried in accordance y with the present invention is to be polymerized, any one of numerous polymerization methods known to those skilled in the art may be used. Catalysts such as metallic oxides'and. organic bases when used in conjunction with reaction solvents such as alkanes, cycloalkanes and aro- Having described the basic aspects of the present invention the following examples are given to illustrate embodiments thereof.

' Example I Pararormal'dehyde having a particle size of 5G to 100 US. mesh and containing about 3% by Weight of water Washeated in a closed reaction vessel to a temperature of 250 C. .The reaction mixture was swept with nitrogen gas. minute of the resultant formaldehyde gas into a second reaction vessel. The second reaction vessel comprisedv a 50 mm. reactor column containing ml. of dimethylsulfoxide which contained'less than 0.1% by weight of Water. The dimethylsulfoxide'was maintained at a temperatureof 85 to 95 .C. while the wet formaldehyde gas from the first reaction vessel was passed into the bottom The dried formaldehyde gas'coming from the top of the second reaction vessel containing the dimethylsulfoxide Was passed into a series of polymerization vessels which contained solution of 0.1 m1. of tri-n-butylamine inv 50 ml. of dry cyclohexane. The polymerization reaction mixtureswere kept at a temperature or 25 to C. As. the dried formaldehyde gas passed into the polymerization vessels, polyoxymethylene polymer precipitated'from the solution. This polymer was isolated by filtration and the reduced specific viscosity '(n sp/c) was determined at 140 C. using a 0.15% solution or the polyoxymethylene in benzyl alcohol containing 1%by weight diphenylamine and.0.05% by weight N,N,N.,N'-tetrakis-(2-h droxypropyl) ethylene diamine. e The result of 5 2-minute runs are tabulated below:

The .nitrogen sweep carried about 1.5 g. per

Example [I In a procedure identical to that outlined in Example I with the exception that the, second vessel containing the dimethylsulfoxi'de Was omitted, formaldehyde gas generated from the first reaction vessel was passed direct- The results of' ly into similar polymerization solutions. two such runs are tabulated below:

Time (min) POM isolated Run On 7 on Wt. (g.) n sp/c 1 V 2 4 0.38 0.16 2'. l0 12 O. 62 0. 14

It is seen from the above specific example that when dimethylsulfoxide is used as the drying agent, a high molecular weight polyoxymethylene polymer is obtained; This'indicates that the water from the initial gas stream is thoroughly and efliciently removed by contact with dimethylsulfoxide. a i I claim: I

1. A method forremoving water from formaldehyde which comprises contacting a gaseous-stream of formaldehyde with dimethylsulfoxide maintainedat a'temperature of 'from about 20 to about C, and separating said formaldehydefrom said dimethylsulfoxide. i

2. A method-tor claim; 1 wherein said dimethylsulfoxide contains a maximum of about 5% by Weight of water.

9). A method of claim 2 wherein said rorrnaldehyde gas coming into contact with dimethylsulfoxide contains up to about 57% by weight of water. 4. A method for removing water iirornformaldehyde which comprises contacting a gaseous stream of formaldehyde containing from up to about 5% by Weight of water with dimethylsulfoxide containing less than-about 5% by weight of water maintained at a temperature from below about 0.1% by weight andv separating said'forme aldehyde gas irom said dimethylsulfoxide.

References Cited by the Examiner UNITED STATES PATENTS 2,365,898 12/44 Morris at al. 7

7 2,780,652 2/ 57 Gander 260-506 5 REUBEN FRIEDMAN, Primary Examiner. 

1. A METHOD FOR REMOVING WATER FROM FORMALDEHYDE WHICH COMPRISES CONTACTING A GASEOUS STREAM OF FORMALDEHYDE WITH DIMETHYLSULFOXIDE MAINTAINED AT A TEMPERATURE OF FROM ABOUT 20 TO ABOUT 100*C., AND SEPARATING SAID FORMALDEHYDE FROM SAID DIMETHYLSULFOXIDE. 